I like pulling a sled for conditioning work, it's never boring and makes me feel like a truck. I generally pull it quite heavy and try to add weight when I can. But every once in a while I will take off a bunch of the weight and pull it much lighter. Using a lighter sled, taking very large steps, and leading with the heel will really fry your hamstrings.

Feel free to add your sled pulling tips to this thread. I am always looking for ways to make the sled more enjoyable and productive.